The present invention relates generally to an amplifier for use in a telephone instrument to increase the volume of received audio signals to aid the hearing impaired and those with normal hearing sensitivity when the telephone is located in environments with high ambient noise levels and deals more specifically with a push-button operated switchable gain control amplifier for use with coin-operated and pay type telephone instruments.
It is well known to provide a telephone amplifier in the handset of a conventional telephone to vary the amplitude of audio signals received from the telephone subset. Generally, an amplifying receiver and a volume control in the form of a potentiometer are located in the handset and a user varies the receiver volume to suit the user's need by rotating the potentiometer. A handset amplifier of the above described general type is disclosed in U.S. Pat. Nos. 4,151,376 and 3,254,160. Another telephone handset amplifier disclosed in U.S. Pat. No. 4,466,120 utilizes a rocker switch located in the handset to control the amplifier to vary the receiver volume.
One problem generally associated with the handset type amplifiers is the volume control potentiometer is often difficult to operate especially for users with a physical handicap or impaired hand and finger movement or limited dexterity, for example, due to arthritis.
Another problem associated with handset type amplifiers is that the volume level set by a previous user may be too loud for the current user possibly subjecting the current user to hearing damage or other uncomfortable hearing sensations if the volume is not reduced prior to the start of the call. Consequently, to avoid such hearing discomfort, a user must remember to check the setting of the volume control at the beginning of the call.
Yet another problem associated with handset amplifiers is the relatively high cost associated with the replacement of a damaged or missing handset. Such replacement costs can be significant especially when the amplifier handset is used with coin-operated or pay type telephone instruments which are frequently located in an environment subject to repeated vandalism wherein the vandalism takes the form of ripping the handset and cord from the telephone housing.
It is desirable therefore to provide a telephone amplifier for use with a coin-operated or pay type telephone instrument wherein the amplifier is located within the telephone instrument housing rendering it relatively vandal proof and thus substantially reducing the cost of handset replacement.
It is also desirable to provide a telephone amplifier that is readily adjustable by a user having a physical handicap or other physical limitation.
An object of the present invention is, therefore to provide a telephone amplifier for use with a coin-operated or pay type telephone instrument that overcomes the above described problems associated with conventional handset amplifiers.